1. Field of the Invention
The present invention relates generally to voltage regulators and, more particularly, to voltage regulators employing an error signal to change the firing angle of a triac delivering voltage to a load.
2. Description of the Prior Art
The triac is a bi-directional semiconductor device which must be "gated" into conduction upon the simultaneous application of a voltage between its two main terminals and a gating signal applied to a gate electrode. The triac begins conducting when a current of sufficient strength is applied to its gate electrode and remains conducting independently of the gate current, from the moment when, and as long as, a current of strength greater than a given threshold flows therethrough between its main electrodes. Removing the voltage from across the main electrodes, as for example when the source voltage crosses the zero axis, normally renders the triac non-conductive.
It is known to use a triac voltage when regulating voltage in an alternating current voltage source. For example, U.S. Pat. No. 4,355,242 issued on Oct. 19, 1982, uses a voltage regulating or control system employing a triac to control the power supplied to a load from an alternating current voltage source. The system utilizes an oscillator to provide pulse train firing of the triac.
U.S. Pat. No 4,766,363 issued Aug. 23, 1988 supplies power from an A.C. source to a load under the control of a power switching triac in response to signals from a feedback loop.
Other examples of alternating current voltage regulators use sawtooth generators tied to the input voltage source. Based on the output voltage delivered to the load, an error signal is produced and used to control the sawtooth waveform.
The above-mentioned devices, however, are unable to maintain a stable RMS output voltage across the load when utilizing an unregulated A.C. input voltage. These devices use a pulse train or feedback signal to control voltage to the load or control a sawtooth waveform to produce a regulated output voltage.
It is, therefore, needed to produce an alternating current voltage regulator which provides improvements over the presently known devices for regulating an input A.C. voltage to deliver a stable RMS output voltage to a load.